You now need to explicitly specify whether flux files get merged or

overwritten, because the old behaviour was weird. Reader uses SqliteFluxSink to
write flux files, rather than raw database accesses.

doc/using.md

@@ -300,13 +300,13 @@ containing valuable historical data, and you want to read them.
 Typically I do this:
 
 ```
-$ fluxengine read brother -s :d=0 -o brother.img --write-flux=brother.flux --write-svg=brother.svg
+$ fluxengine read brother -s :d=0 -o brother.img --write-flux=brother.flux --overwrite --write-svg=brother.svg
 ```
 
-This will read the disk in drive 0 and write out a filesystem image. It'll
-also copy the flux to brother.flux and write out an SVG visualisation. If I
-then need to tweak the settings, I can rerun the decode without having to
-physically touch the disk like this:
+This will read the disk in drive 0 and write out a filesystem image. It'll also
+copy the flux to `brother.flux` (replacing any old one) and write out an SVG
+visualisation. If I then need to tweak the settings, I can rerun the decode
+without having to physically touch the disk like this:
 
 ```
 $ fluxengine read brother -s brother.flux -o brother.img --write-svg=brother.svg

lib/flags.h

@@ -147,7 +147,7 @@ public:
     void set(const std::string& value) { _value = std::stod(value); }
 };
 
-class BoolFlag : public ValueFlag<double>
+class BoolFlag : public ValueFlag<bool>
 {
 public:
     BoolFlag(const std::vector<std::string>& names, const std::string helptext,

lib/fluxsink/fluxsink.h

@@ -4,6 +4,7 @@
 #include "flags.h"
 
 extern FlagGroup hardwareFluxSinkFlags;
+extern FlagGroup sqliteFluxSinkFlags;
 
 class Fluxmap;
 class FluxSpec;
@@ -13,11 +14,9 @@ class FluxSink
 public:
     virtual ~FluxSink() {}
 
-private:
     static std::unique_ptr<FluxSink> createSqliteFluxSink(const std::string& filename);
     static std::unique_ptr<FluxSink> createHardwareFluxSink(unsigned drive);
 
-public:
     static std::unique_ptr<FluxSink> create(const FluxSpec& spec);
 
 public:

lib/fluxsink/sqlitefluxsink.cc

@@ -2,14 +2,37 @@
 #include "fluxmap.h"
 #include "sql.h"
 #include "fluxsink/fluxsink.h"
+#include "flags.h"
 #include "fmt/format.h"
+#include <unistd.h>
+
+FlagGroup sqliteFluxSinkFlags;
+
+static SettableFlag mergeFlag(
+	{ "--merge" },
+	"merge new data into existing flux file");
+
+static SettableFlag overwriteFlag(
+	{ "--overwrite" },
+	"overwrite existing flux file");
 
 class SqliteFluxSink : public FluxSink
 {
 public:
     SqliteFluxSink(const std::string& filename)
     {
+		if (mergeFlag && overwriteFlag)
+			Error() << "you can't specify --merge and --overwrite";
+
+		if (!mergeFlag)
+		{
+			if (!overwriteFlag && (access(filename.c_str(), F_OK) == 0))
+				Error() << "cowardly refusing to overwrite flux file without --merge or --overwrite specified";
+			if (remove(filename.c_str()) != 0)
+				Error() << fmt::format("failed to overwrite flux file");
+		}
 		_outdb = sqlOpen(filename, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE);
+
 		int oldVersion = sqlReadIntProperty(_outdb, "version");
 		if ((oldVersion != 0) && (oldVersion != FLUX_VERSION_CURRENT))
             Error() << fmt::format("that flux file is version {}, but this client is for version {}",

lib/reader.cc

@@ -2,6 +2,7 @@
 #include "flags.h"
 #include "usb.h"
 #include "fluxsource/fluxsource.h"
+#include "fluxsink/fluxsink.h"
 #include "reader.h"
 #include "fluxmap.h"
 #include "sql.h"
@@ -18,7 +19,13 @@
 #include "imagewriter/imagewriter.h"
 #include "fmt/format.h"
 
-FlagGroup readerFlags { &hardwareFluxSourceFlags, &fluxmapReaderFlags, &visualiserFlags };
+FlagGroup readerFlags
+{
+	&hardwareFluxSourceFlags,
+	&sqliteFluxSinkFlags,
+	&fluxmapReaderFlags,
+	&visualiserFlags
+};
 
 static DataSpecFlag source(
     { "--source", "-s" },
@@ -61,7 +68,7 @@ static SettableFlag highDensityFlag(
 	{ "--high-density", "--hd" },
 	"set the drive to high density mode");
 
-static sqlite3* outdb;
+static std::unique_ptr<FluxSink> outputFluxSink;
 
 void setReaderDefaultSource(const std::string& source)
 {
@@ -86,8 +93,8 @@ void Track::readFluxmap()
 		"{0} ms in {1} bytes\n",
             int(fluxmap->duration()/1e6),
             fluxmap->bytes());
-	if (outdb)
-		sqlWriteFlux(outdb, physicalTrack, physicalSide, *fluxmap);
+	if (outputFluxSink)
+		outputFluxSink->writeFlux(physicalTrack, physicalSide, *fluxmap);
 }
 
 std::vector<std::unique_ptr<Track>> readTracks()
@@ -100,17 +107,8 @@ std::vector<std::unique_ptr<Track>> readTracks()
 
 	if (!destination.get().empty())
 	{
-		outdb = sqlOpen(destination, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE);
 		std::cout << "Writing a copy of the flux to " << destination.get() << std::endl;
-		sqlPrepareFlux(outdb);
-		sqlStmt(outdb, "BEGIN;");
-        sqlWriteIntProperty(outdb, "version", FLUX_VERSION_CURRENT);
-		atexit([]()
-			{
-				sqlStmt(outdb, "COMMIT;");
-				sqlClose(outdb);
-			}
-		);
+		outputFluxSink = FluxSink::createSqliteFluxSink(destination.get());
 	}
 
 	std::shared_ptr<FluxSource> fluxSource = FluxSource::create(spec);